Apache Felix OSGi logging with Logback

Question

My current application uses Logback for logging. I have used Apache Felix to deploy an OSGi framework that allows bundles to be dynamically registered at runtime. The Felix setup is as follows:

    ...

    //System.out.println("Building OSGi Framework");
    FrameworkFactory frameworkFactory = ServiceLoader.load(FrameworkFactory.class).iterator().next();
    Map<String, String> config = new HashMap<>();

    // specify the class loader
    config.put(Constants.FRAMEWORK_BUNDLE_PARENT, Constants.FRAMEWORK_BUNDLE_PARENT_FRAMEWORK);

    // specify the osgi cache directory
    config.put(Constants.FRAMEWORK_STORAGE, appConfig.getOsgiCacheDir());

    // make sure the cache is cleaned
    config.put(Constants.FRAMEWORK_STORAGE_CLEAN, Constants.FRAMEWORK_STORAGE_CLEAN_ONFIRSTINIT);

    // expose api
    config.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA, "list.of.packages.to.export");

    // more properties available at: http://felix.apache.org/documentation/subprojects/apache-felix-service-component-runtime.html
    config.put("ds.showtrace", "false");
    config.put("ds.showerrors", "true");
    config.put("felix.fileinstall.dir", appConfig.getActiveOsgiExtDir());
    config.put("felix.fileinstall.tmpdir", appConfig.getTempOsgiExtDir());
    config.put("felix.fileinstall.bundles.startTransient","true");
    config.put("felix.fileinstall.poll","5000");
    config.put("felix.fileinstall.bundles.new.start", "true");

    LOG.debug("OSGi config: " + config.toString());

    framework = frameworkFactory.newFramework(config);

    try {
        framework.init();
        FrameworkEvent event;

        do {
            framework.start();
    ...

The only problem is that there seems to be no logging with Felix. When a bundle fails to load for some reason I can't see why! I know that I can use the following in the bundle to obtain the parent logger:

ServiceReference ref = bundleContext.getServiceReference(LogService.class.getName());
if (ref != null) {
    LogService log = (LogService) bundleContext.getService(ref);
    ...
   }

However, I don't understand how I can get felix to use logback as the logger in the first place.

Answer 1

I guess you use Apache Felix Log to have a LogService in you OSGi container. Apache Felix Log implements the chapter " 101 Log Service Specification " of OSGi Enterprise Specification.

The basic of LogService implementation stores the logged entries for a while but does not write them to anywhere. You can query the recorded entries via LogReaderService or LogListener .

On the other hand, you might use Logback in the way that you added slf4j-api and slf4j-logback to your OSGi container. By doing that, everything that is logged via slf4j-api classes will be logged by logback.

If my guesses were right, the osgi-loglistener-slf4j bundle could help you. This bundle does nothing else but registers a LogListener for every LogReaderService in the environment and forwards every log entries it catches to slf4j-api . The bundle is available on maven-central

If you do not want to use slf4j API, you can write a similar bundle that does the log forwarding from LogReaderService to Logback . If you check the source of the bundle I linked, you will see that it is implemented with only a few lines of code.